The invention is based on a fuel supply system for furnishing fuel for an internal combustion engine and to a method for operating an internal combustion engine.
Until now, there have been fuel supply systems in which a first fuel pump pumps fuel from a fuel tank to a second fuel pump via a fuel connection. The second fuel pump in turn feeds the fuel via a pressure line to at least one fuel injection valve. Typically, the number of fuel injection valves is equal to the number of cylinders of the engine. The fuel supply system may be constructed such that the fuel injection valves inject the fuel directly into an engine combustion chamber. In operation of this fuel supply system, high pressure in the pressure line leading to the fuel injection valve is necessary. For safety reasons, and because leakage of the fuel injection valve into the combustion chamber can never be entirely precluded, it is expedient after the engine has been turned off to reduce the pressure in the fuel connection and in the pressure line of the fuel supply system completely, or at least extensively.
If the pressure is extensively or entirely reduced in the fuel supply system while the engine is shut off, then a vapor bubble can form in the fuel connection between the first fuel pump and the second fuel pump, or in the pressure line between the first fuel pump and the fuel valve. The size of the vapor bubble, or the number and size of individual bubbles in the vapor bubble, depends among other factors particularly on the temperature prevailing in the engine compartment after the engine has been shut off. The vapor bubble must be scavenged from the lines or compressed before the engine is next started again. Since the supply quantity of the second fuel pump is relatively low during starting of the engine, it takes a long time until the vapor bubble in the pressure line is compressed. The result is long starting times for turnover of the engine. Since the vapor bubble is especially large when the engine compartment temperature is high, it takes an especially long time to start the engine when the engine compartment temperature is high.